Deep Imaging Search for Planets Forming in the TW Hya Protoplanetary Disk with the Keck/NIRC2 Vortex Coronagraph

Abstract

Distinct gap features in the nearest protoplanetary disk, TW Hya (distance of 59.5 ± 0.9 pc), may be signposts of ongoing planet formation. We performed long-exposure thermal infrared coronagraphic imaging observations to search for accreting planets, especially within dust gaps previously detected in scattered light and submillimeterwave thermal emission. Three nights of observations with the Keck/NIRC2 vortex coronagraph in L′ (3.4-4.1 μm) did not reveal any statistically significant point sources. We thereby set strict upper limits on the masses of nonaccreting planets. In the four most prominent disk gaps at 24, 41, 47, and 88 au, we obtain upper mass limits of 1.6-2.3, 1.1-1.6, 1.1-1.5, and 1.0-1.2 Jupiter masses(M J ), assuming an age range of 7-10Myr for TW Hya. These limits correspond to the contrast at 95% completeness (true positive fraction of 0.95) with a 1% chance of a false positive within 1″ of the star. We also approximate an upper limit on the product of the planet mass and planetary accretion rate of M M M 10 yrimplying that any putative ∼0.1 M J planet, which could be responsible for opening the 24 au gap, is presently accreting at rates insufficient to build up a Jupiter mass within TW Hya's pre-main-sequence lifetime.

Detectability of embedded protoplanets from hydrodynamical simulations

“…Observations using the Keck/NIRC2 vortex coronagraph were performed by Ruane et al (2017) searching for pointsources in the TW Hya disc. This system is the closest known protoplanetary disc to us (60.2 AU, Gaia Collaboration et al 2018), with a central star of 0.7-0.8 M (Andrews et al 2012;Herczeg & Hillenbrand 2014) relatively old (7-10 Myr, Ruane et al 2017), and with an estimated total disc mass of 0.05 M (Bergin et al 2013). The surface gas density has been modelled from ALMA line emission observations (Kama et al 2016;Trapman et al 2017).…”

“…The instrument allows for IR high-contrast imaging in L-band, using angular differential imaging (ADI) Figure 13. Contract curves in L-band for planets embedded in TW Hya, including 95% significance detection limits of Keck/NIR2 observations (Ruane et al 2017). The contrast limits are shown for angular differential imaging (ADI) and reference star differential imaging (RDI).…”

“…The apparent magnitude of the central star is L = 7.01 mag, taken from the W1 band in the WISE catalogue (Wright et al 2010). The coloured regions for each planet model are delimited by the estimated ages (7-10 Myr, Ruane et al 2017). The grey vertical lines account for the gaps observed in Andrews et al (2016) and van Boekel et al (2017).…”

Data Reduction and Image Reconstruction Techniques for Non-redundant Masking

“…Close to the star, the small number of image elements causes small number statistics that degrade the achievable contrast (e.g., Mawet et al 2014). These factors combine to limit achievable coronagraph performance to λ/D (e.g., Mawet et al 2012;Ruane et al 2017).…”

Keck Planet Imager and Characterizer (KPIC): status update

“…The NIRC2 L-band vortex enabled the discovery of new protoplanet candidates, 6, 7 disks, 8 and allowed us to constraint mass accretion rates in protoplanetary disks with gaps. 9 …”